Platelets are a biosubstance that is essential for hemostatic action upon bleeding, and in the case where the function thereof is exhibited excessively, thrombus is formed to cause critical diseases, such as myocardial infarction, cerebral infarction and the like. In the case where platelets fail to function, on the contrary, bleeding tendency is induced. Accordingly, for performing health management and medical treatment, it is important to comprehend the state of platelets in blood by evaluating the function thereof (measurement of aggregation capacity of platelets).
The aggregation capacity of platelets is generally measured in such a manner that aggregation of platelets is induced by adding an aggregation inducing substance, such as collagen and the like, to platelet-rich plasma under a low shear rate, and the transmittance increased by the aggregation is measured.
Collagen of animal origin is generally used for measuring aggregation capacity of platelets, and there are known ones that induce aggregation of platelets in artificially synthesized collagen.
Non-patent Document 1, 2 and 3 disclose a polypeptide -(Gly-Pro-Hyp)10- having a triple helix structure and a substance obtained by crosslinking the polypeptide to form a quaternary structure, and also disclose the platelet aggregation inducing activity of the substances.
The polypeptide -(Gly-Pro-Hyp)10- disclosed in the non-patent documents has low platelet aggregation inducing activity and cannot be used for measuring aggregation capacity of platelets.
The substance obtained by crosslinking the polypeptide to form a quaternary structure has higher platelet aggregation inducing activity as compared to the polypeptide and can be used for measuring aggregation capacity of platelets. For obtaining the substance, however, it is necessary to perform peptide synthesis reaction including repeated deprotection and formation of amino acid bond, and it is also necessary to perform crosslinking. Repetition of the reactions decreases the yield of the target reaction product. The decrease in yield results in increase of cost.    [Non-patent Document 1] THE JOURNAL OF BIOLOGICAL CHEMISTRY, May 13, 1994, 269(19), 13899-18903    [Non-patent Document 2] The Biochemical Journal, 1995, 306, 337-344    [Non-patent Document 3] Cardiovascular Research, 1999, 41, 450-457